I've always heard that you don't want to top, chop, or do anything to the girls when they've started to flower. You will diminish your yield and temporarily stress the plant. You want as little stress in this period as possible because you want her to focus on budding, not healing.
If you have a height problem I'd suggest tying them back or something less drastic. However, some people do take off everything but the main colas a few weeks into flower so most of the budding is concentrated to a few sites.